The research is all pointing in one direction: Whether you believe humans are contributing to it, or not, climate change is happening, and it's going to cost us. But how much?

We scoured the history books for clues as to what happens to advanced civilizations when the climate they're used to stops behaving the same way.

Here are six cultures that simply couldn't cope.

The Indus Valley Civilization

The Indus Valley Civilization, sometimes called the Harappan Civilization, was one of the world’s first, flourishing in what is now Pakistan and northwestern India more than 4,000 years ago. And chances are, you might not even have heard about it until recently, because when it collapsed, it completely vanished from the historical record.

Image: NASA

At the same time as the Egyptians and Sumerians were spreading their influence over the Middle East, the Harappans developed sophisticated pottery and artwork, and built large and well-organized cities all along the Indus valley, collectively accounting for up to 10 per cent of the entire global population at the time.

But of the Harappans themselves, we know nothing. The end of their civilization was so total, we didn’t even know about them until the 20th Century, and even then we’ve still not deciphered their written language, so we have no names or stories.

What we do know is climate change was a huge factor in their demise. Archaeologists surmise the Harappans developed their civilization in a climatic sweet spot of only 2,000 years, a window that began closing in the 22nd Century B.C.E.

That, according to scientists, is when the monsoons that watered the region became irregular, sparking a 200-year drought. As crop yields fell, the Harappans’ society began to fragment, and recent research indicates that disease levels and the rate of violent death were at the peak just as the ancient cities were in an advanced stage of abandonment.

Sooner or later, someone will figure out how to read their writing and see how the relatively abrupt shift in climate may have influenced their culture. Until then, for stronger evidence of the role of climate change in civilizations' collapse, we’ll turn our eyes westward where one of the greatest ancient empires was finding out what happens when the rain refuses to cooperate.

The Akkadian Empire

Unlike the Harappans, we know exactly what the Akkadians, in their domains in the Fertile Crescent, thought when their region entered a dry period lasting decades of centuries.

The Akkadians roared onto the scene more than 4,000 years ago, conquering city after city until their empire stretched the Persian Gulf up to the mountains where the great Tigris and Euphrates rivers start their journey as streams.

During the sack of one such city, Nippur, Akkadian troops supposedly violated the temple of one of their gods. The entire pantheon got together and decided to make the Akkadians pay for their offence.

The famine was too much for the Akkadians’ sophisticated system of irrigation and food storage. Whole cities had to be abandoned, streaming southward and swelling the capital and other cities with refugees, more mouths to feed at a time when there wasn’t enough to go around.

Image: US Army

The famine and resulting social unrest weakened the empire enough that it crumpled easily before invaders from the north. And given the generally arid conditions and heavy reliance on irrigation in today’s Middle East, the Akkadian collapse could be a chilling glimpse of the unrest that could ensue if the modern-day region suffers a similar drought.

The Minoans

It hardly seems worth it for an ancient civilization to reach staggering levels of advancement: It always seems like some kind of horrific catastrophe awaits them.

Enter the Minoans, a civilization centred on the island of Crete, reaching incredible heights of sophisticated development and artwork. They are credited as one of the first civilizations to invent a system of writing (and one of their two main scripts still hasn’t been deciphered), and their trading links are said to have spanned the eastern Mediterranean.

As for their fate, it looks like they got hit with a double whammy. Climatic research seems to suggest the island culture started feeling the sting of centuries of strong El Nino events from around 1450 B.C., coinciding with the Minoans’ decline.

Then the volcano on the Aegean island of Thera (now Santorini) blew its top, also around the mid-second-millenium B.C. While the tsunami alone would have devastated coastal communities, the incredibly powerful blast would have ejected enough material into the air to usher in years of colder, wetter summers.

Image: NASA

It was probably a combination of these two catastrophes, one instantaneous, the other slow-moving, that took down the Minoans. The island was conquered by invaders from mainland Greece, and never achieved prominence again.

The Maya

Here, in the meantime, is an advanced American civilization, and unlike the others on this list so far, their climate change-induced collapse may have been at least partly of their own doing.

The Maya are actually both an exemplary and cautionary tale of adaptation. Around 2,000 years ago, a rise in sea levels swamped coastal farms, according to this research. So the Maya simply moved inland, or reclaimed the farms for wetland agriculture.

Image: Pavel Sigarteu

The system fed the burgeoning Maya population adequately, but a centuries-long wet period beginning from the 440s to 660s A.D. really propelled the civilization to prominence.

An advanced culture bloomed in dozens of sophisticated cities, the largest ones boasting around 70,000 people and easily rivaling most of Europe’s communities at the time. Philosophy and science also blossomed – these are the people who invented the Long Count calendar, after all.

Then climate patterns shifted, and until around 1,000 A.D., a drying trend slowly led to declining crop yields and increased warfare. A drought in the first century of the 2nd Millennium dealt the death blow. The Maya people still exist, scattered across Mexico, Guatemala and Belize, but their huge cities were long abandoned by the time Spanish Conquistadors arrived in the 1500s.

In this case, though, the Maya may actually have sped up their own demise. Massive urban development led to wide-scale deforestation, reducing atmospheric moisture by 5-15 per cent. Doesn’t sound like a lot, but this research says that could have accounted for 60 per cent of the drying of the region during the collapse.

A professor quoted in this National Geographic article warns against relying too much on this example as an indicator of what might happen in the region if if the same drying out happens today – our modern societies are radically different from the classical Maya.

Still, the incredible impact that kind of deforestation had on the area is worth studying, and keeping in mind, as we consider the human factor in climate change.

Cahokia

Almost a thousand years ago, the community of Cahokia on the Mississippi in southwestern Illinois was booming. Its inhabitants built massive earthen mounds, relied on an extensive farming complex for support, and thronged walkways tens of thousands strong, easily dwarfing most European capitals at the time.

Image: Skubasteve834 / Wikimedia Commons

But by 1300 A.D., everybody had apparently packed up and left. What went wrong?

Base on tree ring analysis in the area, the theory is the rapid development of the site coincided with one of the wettest periods in the area, between 1050 and 1100, enough to sustain a massive agricultural revolution.

Easy come, easy go. From 1100, the region suffered 150 years of drought cycles. One drought is said to have lasted 15 years. The civilization had reached a peak under a particular set of climate conditions. When those changed for the worse, the results were predictable.

With falling crop yields, the population plummeted. In 1200, it was half what it was at the peak, and by 1350, the site was all but abandoned.

As with other civilizations suffering the same fate, there’s evidence of massive and rising social unrest. The 20,000 log palisade wall the city’s rulers built is not the kind of decoration you’d expect in a civilization in a golden age of peace and harmony.

By the time European explorers reached the region, all that remained of the largest pre-contact concentration of indigenous people north of Mexico were the huge earth mounds they’d left behind.

Greenland

Everyone knows the story of the Viking landing in Newfoundland, but even before then, Scandinavians were setting in Greenland, building what, at its peak, was a thriving colony that lasted almost 500 years.

This wasn’t a blasted outpost: Up to 5,000 people may have called Greenland home, along with dozens of churches, numerous farms and even bishops.

Image: National Gallery of Oslo / Wikimedia Commons

All was well, so long as the climate cooperated. While more temperate than today, according to Archaeology Magazine, ice-core samples from the 1990s show a definite cooldown beginning in the mid-twelfth century. By the 1500s, the colony was basically gone

Although the cooldown meant an end to the farming and husbandry they were used to, research by a Danish-Canadian team shows they simply turned to the sea, and quite rapidly, with seafood eventually making up 80 per cent of their diet.

Although life in Arctic-like climes is hard, it needn’t mean the end of settlement (just ask the Inuit, with whom the Greenlanders came into occasional content). The Norse settlers were simply too set in their ways, even refusing to adapt the hunting methods and clothing of the Inuit.

Image: Frederik Carl Peter Rüttel

Add to that more treacherous trade routes due to increased sea ice, falling demand for their exports, and a growing sense of isolation from their cultural counterparts in Europe, and you have plenty of reasons for young Greenlanders to leave the colony.

The island was abandoned by Europeans by 1500, although eventually Denmark would take possession of it. It is now a Danish territory, with substantial home rule.